The present invention relates to vehicle cruise control systems and more particularly to a unique device for modulating constant speed cruise control systems.
A wide variety of cruise or speed control systems have been proposed for maintaining the speed of a vehicle fairly constant. Such systems automatically vary the throttle position of the carburetor in response to changing load conditions to maintain a constant set speed. Typical commercially available systems include a speed sensor which senses actual vehicle speed and generates a signal which is transmitted to an electronic logic circuit or module. The module compares actual vehicle speed with a desired or "set" speed and generates a control signal which is transmitted to a vacuum servo transducer or control unit. The transducer is typically a valve structure interposed between a vacuum storage tank or a line connected to the engine intake manifold and a vacuum actuator. The vacuum actuator is connected to the vehicle throttle linkage. If the sensed speed is below the set speed, the servo transducer will "open" and vacuum from the storage tank will be applied to the vacuum actuator causing the throttle to open until the "set" speed is reached and/or to maintain the set speed.
When a rapid increase in load occurs, such as when the vehicle approaches a steep incline, typical cruise control systems produce a somewhat violent throttle position change. This violent change can actuate the accelerator pump or enrichment circuits of the carburetor resulting in excessive fuel flow to the intake manifold. This causes inefficient engine operation and a fairly rapid decrease in the intake manifold vacuum level.
Under constant or steady state load conditions, vehicle cruise control devices tend to increase fuel efficiency. Operator induced speed changes which have an adverse effect on fuel efficiency are avoided. However, under increasing load conditions, besides the occurrence of violent throttle position changes, the cruise control systems will reduce intake manifold vacuum levels, through throttle opening, in an attempt to maintain vehicle speed. This also results in a decrease in engine operating efficiency. Examples of automatic vehicle speed or cruise control systems of the aforementioned type may be found in U.S. Pat. No. 3,485,316, entitled AUTOMOBILE SPEED CONTROL and issued on Dec. 23, 1969, to Slavin et al and U.S. Pat. No. 4,170,274, entitled DEVICE FOR REGULATING THE TRAVELING SPEED OF A MOTOR VEHICLE and issued on Oct. 9, 1979, to Collonia.
The intake manifold vacuum level of a spark ignition internal combustion engine is proportional to and a direct indicator of operating or fuel efficiency. An internal combustion engine operates most efficiently under conditions of high intake manifold vacuum. During rapid acceleration and/or high load conditions, intake manifold vacuum levels will drop causing inefficient operation.
Various proposals have been made to indicate to the operator when the vehicle is being operated in an efficient range of intake manifold vacuum levels. One such device is merely a vacuum gauge which delineates efficient and inefficient "areas" of operation. The gauge would be mounted in the vehicle compartment and directly indicates intake manifold vacuum levels. The operator attempts to "modulate" or control depression of the accelerator to maintain intake manifold vacuum levels at the "high" range to thereby increase fuel efficiency.
Intake manifold vacuum level sensors have also been electrically connected to a light signaling device which turns "on" during inefficient vehicle operation. Such devices, of course, have no effect on the operation of an automatic cruise control system which may be incorporated in the vehicle.
Other devices have been proposed which actively indicate inefficient vehicle operation in response to a reduction in intake manifold vacuum levels. These devices sense the intake manifold vacuum level and generate a force which tends to close the throttle valve and create an increased resistance to accelerator movement. An example of one such device may be found in U.S. Pat. No. 4,026,255, entitled VEHICLE ENGINE SIGNAL DEVICE and issued on May 31, 1977, to Weiler, Jr. The device disclosed therein includes a piston cyclinder type actuator which is connected to the throttle linkage and is shifted in response to the change in intake manifold vacuum levels. When a "low" vacuum level is encountered, the actuator tends to close the throttle causing increased resistance to depression of the accelerator and thereby actively signaling inefficient vehicle operation. Examples of other such signaling devices may be found in U.S. Pat. No. 2,148,729, entitled CARBURETOR THROTTLE CONTROL and issued on Feb. 28, 1939, to Coffey; U.S. Pat. No. 2,692,980, entitled ENGINE CONDITION SIGNAL ARRANGEMENT FOR AUTOMOTIVE VEHICLES and issued on Oct. 26, 1954, to Platt; U.S. Pat. No. 2,825,418, entitled MOTOR VEHICLE ACCELERATION SIGNAL DEVICE and issued on Mar. 4, 1958, to Kershman; and U.S. Pat. No. 3,958,542, entitled THROTTLE CONTROL APPARATUS USING PEDAL RESISTANCE and issued on Mar. 25, 1976, to Tanner.
With compression ignition or diesel internal combustion engines which are fuel injected, fuel flow rates are controlled by throttle position. Efficiency of operation and hence maximization of fuel economy is directly proportioned to throttle position. Intake manifold vacuum levels in a diesel are essentially nonexistent. As a result, signaling devices of the aforementioned type would not properly indicate inefficient vehicle operation. Automatic, constant speed cruise control systems which have been used with diesel engines do not optimize fuel efficiency under increasing load conditions. Typical diesel cruise control systems are of the same type as have been used on spark ignition engines and which are described above. Such engines include, however, a mechanically driven vacuum pump as a vacuum source.
A need exists for a device and system which will allow a variable vehicle speed within preset limits under light and moderate load conditions but will seek to maintain intake manifold vacuum levels at or above a preset point or throttle positions at or below a preset point to increase efficiency of engine operation when increased and/or high load conditions are experienced. Such a system should also soften or moderate the rapid and wasteful throttle movements which have heretofore been experienced with automatic cruise control systems.